The present invention relates to a lithium ion secondary battery, and more specifically, to a cylindrical lithium ion secondary battery equipped with a winding type electrode.
In recent years, portable and cordless electronic appliances including AV devices and personal computers are being developed in a rapid pace, and lithium ion secondary batteries are being used as a power supply for driving these appliances because the batteries have characteristics of being small, lightweight and having a high-energy density.
Among the lithium ion secondary batteries, a cylindrical lithium ion secondary battery is disclosed in Japanese Patent Publication No. 3143951 where a metallic center pin in the form of a hollow cylinder is arranged at the center space of the winding type electrode in order to maintain high safety standards even when a high pressure is applied to the battery from outside.
The batteries with this structure can be used as consumer-oriented batteries such as personal computers and cellular phones, but it is not appropriate to use them in electric vehicles and electric tools that cause somewhat large vibrations. This is because the electrode group, which is not fixed, is highly likely to be damaged while moving around inside the battery case. For example, the foil may be cut.
On the other hand, another lithium ion secondary battery is disclosed in Japanese Laid-Open Patent Publication No. 2001-216949, where a protruding element member having the same diameter as the inside diameter of the battery can, is placed in either both ends or one end of the electrode group and the protruding member is fixed in a core member made of polypropylene or the like. This structure prevents the winding type electrode from moving around in the battery case so as to achieve high assembling precision.
However, in order to fabricate a battery having such a structure, the protruding member is inserted while the projecting part of the protruding member is being inserted into a small hole in the center of the core member and the protruding outer region of the protruding member is being inserted in tight contact as a whole with the inner wall of the battery case. This deteriorates workability in the fabrication of the battery and makes it harder to assemble the battery.
In view of the aforementioned conventional problems, the present invention has an object of fixing the electrode group smoothly, thereby reducing the probability of the electrode group moving around in the battery to be damaged when the battery is dropped or shocked.
The present invention relates to a cylindrical lithium ion secondary battery comprising:
a safety valve;
an electrode group comprising a band-shaped positive electrode plate and a band-shaped negative electrode plate which are wound together with a separator disposed therebetween; and
a bottomed cylindrical metal battery case accommodating the electrode group together with a top insulator plate,
the top insulator plate being designed to be elastic and provided in the center thereof with a through hole into which a center core member is press-fitted.
In this cylindrical lithium ion secondary battery, it is preferable that a plurality of protruding parts are provided on the outer peripheral surface of the top insulator plate, and that the tips of the protruding parts are in tight contact with the inner wall of the battery case.
In the top insulator plate, the diameter of a virtual circle formed by connecting the tips of the protruding parts before the press-fitting of the center core member is preferably 1 to 1.05 times the inner diameter of the metal battery case.
The top insulator plate preferably has a slit around the through hole.
The top insulator plate is preferably made of plastic.
The center core member is preferably made of metal.
It is preferable that the center core member is in the form of a hollow cylinder, and that at least one end of the center core member is a tapered or sharp end.
The center core member can have a slit extending in the longitudinal direction thereof.
The present invention also relates to a method for fabricating a cylindrical lithium ion secondary battery comprising the steps of:
(a) preparing an electrode group by winding a band-shaped positive electrode plate and a band-shaped negative electrode plate together with a separator disposed therebetween, and accommodating the electrode group into a bottomed cylindrical metal battery case;
(b) arranging a top insulator plate on the end surface of the electrode group, the top insulator plate being designed to be elastic and provided with a through hole at the center thereof; and
(c) press-fitting a center core member into the through hole to fix the electrode group in the metal battery case.
In this fabrication method, it is preferable that a plurality of protruding parts are formed on the outer peripheral surface of the top insulator plate and that the diameter of a virtual circle formed by connecting the tips of the protruding parts before the press-fitting of the center core member is 1 to 1.05 times the inner diameter of the metal battery case.
While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.